This invention relates to electronic valve control systems and more particularly to electronic throttle control systems for internal combustion engines with low friction default mechanisms.
Valve assemblies for engines and related systems typically utilize rotatable valve members in fluid flow passageways to assist in regulating fluid flow through them. For example, throttle valve members are positioned in the air induction passageways in internal combustion engines. The valve assemblies are controlled either mechanically or electronically and utilize a mechanism which directly operates the valve member.
For electronic throttle bodies (ETB) or electronic control systems (ETC), it is desirable to have a failsafe mechanism or system which activates the throttle valve in the event that the electronic control or electronic system of the vehicle fails. There are several known electronic throttle control systems which utilize default (xe2x80x9cfailsafexe2x80x9d) mechanisms for closing the throttle valve or moving it to a slightly open position in the event of an electronic failure in the vehicle. It is desirable to minimize or reduce the frictional forces in the operation of the electronic throttle control system in order to allow the system to operate more accurately and not bind or jam. Reducing friction is important in the operation of the ETC since high friction increases gear loading and motor currents. Additionally, friction makes the ETC more difficult to control electronically as the mechanical system will become less predictable. For example, when the ETC controller issues a command, a specified motor current is issued and a particular throttle angle is expected in return. Depending on the magnitude of the requested change in plate angle, the controller calculates an expected overshoot error. Friction can make the overshoot unpredictable and the controller will have to take extra steps to correct the unexpected angle that it receives in place of the command angle.
Plunger mechanisms used in failsafe (default) mechanisms are typically made of all metal components which have high friction forces in operation and have the tendency to bind or jam. They also typically have large load differentials, that is the difference between the initial force to depress the plunger and the final force.
It would be desirable to have an electronic valve control system with an improved failsafe or limp-home mechanism and which minimizes the frictional forces in the default mechanism. It would also be desirable to have an ETC system which utilizes a plunger-type default mechanism which does not have the tendency to bind or jam and which has low friction forces.
The present invention provides an electronic throttle control assembly having a housing with a gear train and throttle valve mechanism. A throttle plate is positioned on a throttle shaft and the plate and shaft are positioned in the engine or air induction passageway, such that the throttle plate regulates airflow into the engine. A cover member enclosing the gear train contains a motor with a spur gear.
The operation of the throttle valve is accomplished through the gear train assembly which is driven by the motor. The motor is regulated by the electronic control unit of the vehicle which in turn is responsive to the input of the vehicle operator or driver. A throttle position sensor responsive to the rotation of the throttle shaft feeds back the position of the throttle plate to the electronic control unit.
In the operation of the throttle valve, a gear connected to the motor operates an intermediate gear (or idler gear), which in turn operates a sector gear which is connected to the throttle body shaft. The sector gear is biased by a spring member toward the closed position of the throttle valve. As a failsafe or default mechanism, a spring-biased plunger member is attached to the housing and positioned to interrupt operation of the sector gear in the event of an electronic failure and prevent the throttle valve from closing completely. At the default position, the vehicle can still be operated, although at a reduced capacity. This allows the driver to xe2x80x9climp-home.xe2x80x9d
If the throttle valve is in its closed position when an electronic failure occurs, the spring-biased plunger member acts on the sector gear to open the throttle valve slightly to the failsafe position.
In order to minimize frictional forces in the plunger mechanism, the spring member and/or plunger member are configured to make as little contact with each other as possible. For this purpose, an xe2x80x9chour-glassxe2x80x9d shaped spring member can be provided. Also, the plunger member can have a ribbed shape or a reduced outer periphery cross-section. It is also possible to make components of the default mechanism from a composite material which is impregnated with a lubricant, such as PTFE. By minimizing the sliding contact and friction between the plunger member and the spring member, the operation of the default mechanism is enhanced.
Other features and advantages of the present invention will become apparent from the following description of the invention, particularly when viewed in accordance with the accompanying drawings and appended claims.